Most common complications associated with Rubella vaccine occur in adult women and are manifested in polyarthraliga and arthritis, associated with RV persistence and localized viral replication. Further, in a recent Institute of Medicine , US National Academy of Sciences meeting (1996) on Vaccine Associated Adverse Reactions, it was recommended that new strategies must be developed for live viral vaccines so as to reduce the incidence of adverse reactions associated with such vaccines. Therefore, there is a need for a "replication -crippled " RV vaccine which is free of adverse reactions. Recently, we have shown that the cause of adverse reactions with live virus vaccine could probably be due to interaction of host proteins with RV cis-acting elements. The host proteins (calreticulin and La) are known autoantigens and patients with natural RV infection develop significant anti-La response following prolonged infection. In addition, we have observed that rubella virus non-structural proteins have domains which interact with cell cycle regulatory protein i.e. retinoblastoma protein (RB) both in vivo and in vitro. This interaction could result in the alteration in cell growth upon RV infection and may be the probable cause of RV induced teratogenesis. For this reason we are developing following strategies to make a "replication-crippled" rubella virus vaccine. 1. Construct a RV infectious plasmid that has altered sites/regions which interact with either calreticulin or La proteins in such a way that RV RNA can replicate at sub optimal level and be eliminated by dilution effect after a few cycles. 2. Alter the RB interacting site(s) in the RV non-structural proteins so that the virus generated from such an RNA may invoke immune response but not result in vaccine related adverse reactions. By combing the above mentioned approaches, our ultimate goal is to create a recombinant "suicide" RV vaccine that contains mutations in host cell binding proteins and is free of adverse reactions. PROGRESS Developed several poorly replicating RV clones using recombinant DNA methods to target mutations in the Rb-binding motif of Rb NSP90. These recombinants werebe tested for their attenuation characteristics in vero 76 cell line. Recently we have identified the Complement 1 protein's "globular head" receptor as another rubella virus interacting host protein. This interaction could play a mojor role in elucidating the transient/chronic arthritis associated with rubella virus vaccine and natural infections.